As per the beta book, "all crystals used in lightsabers are some form of Kyber crystal." The basic idea is that, in order to handle the energies associated with being the core of a lightsaber, a Kyber crystal has a unique crystalline structure. My big question is, does a Kyber crystal have this structure, or does having this structure make a crystal Kyber?
The reason I ask is because one of my players has taken Force Sensitive Exile and, being Corellian, she carries her father's soul diamond on a necklace. She's mentioned to me that it would be cool if that soul diamond could be used later as her lightsaber crystal, but she's also deferred to my ruling.
My first response is, "Hell yes, that would be awesome!" But I don't know if a soul diamond could have the right make-up. I haven't found anything in canon to say that it couldn't be, except for the maddening implied tautology of "a crystal is Kyber because it is a Kyber crystal."
I'm also unsure of whether or not I want the soul diamond to be her lightsaber crystal. Another thing she and I have discussed is her belief that, if using a soul diamond as a lightsaber crystal and the person who became the diamond was Force sensitve, she might be able to communicate with the soul of the dead person through the Force. This is also a wicked cool idea, but I've already decided that her father wasn't Force sensitive -- her mother was.
So should I let this cool idea slide as proposed? Should I make it so that, yes, the soul diamond of a Force user can be used as a lightsaber crystal, but she's not carrying the right diamond? Or should I say no, that only a Kyber crystal can be a Kyber crystal?
The title of this thread comes from the wisdom I sought from The Bard:
What's in a Kyber crystal? that which we call a lightsaber
With any other crystal would cut just as deep